I would say its worth it, its got better performance enough to justify the extra amount, and has a better igpu build in.
Non-K sklyake chips are overclockable, but the means to do it are un official. If your getting a cheap Asrock Z170 board, get an Asrock one, other manafucatures are complying with Intel and the Non-k overclocking will be shutdown soon or already shut down on some motherboards, while Asrock is a rebel, the gaurantee it too work on their Z170 mobos as they want to keep it alive. Also, if your going to pick up a Z170 mobo to overclock it, dont forget to also pick up fast memory like 2666Mhz or 2800Mhz as faster DDR4 memory with the i3 6100 is very beneficial to gaming.